Naturally occurring Brookhaven National Laboratory Interactive Table of Nuclides for a more accurate reading.

Much of the past work on measuring the isotopic composition of Fe has centered on determining 60Fe variations due to processes accompanying nucleosynthesis (i.e., meteorite studies) and ore formation. In the last decade however, advances in mass spectrometry technology have allowed the detection and quantification of minute, naturally occurring variations in the ratios of the stable isotopes of iron. Much of this work has been driven by the Earth and planetary science communities, although applications to biological and industrial systems are beginning to emerge.[1]

Standard atomic mass: 55.845(2) u.


54Fe is observationally stable, with a branching theory that it decays to 54Cr, with a half-life of more than 3.1x1022 years via double electron capture (2β+). All other natural isotopes are known to be stable, which makes 54Fe seemingly strange.


Main article: Iron-56

The isotope 56Fe is the isotope with the lowest mass per nucleon, 930.412 MeV/c2, though not the isotope with the highest nuclear binding energy per nucleon, which is nickel-62.[2] However, because of the details of how nucleosynthesis works, 56Fe is a more common endpoint of fusion chains inside extremely massive stars and is therefore more common in the universe, relative to other metals, including 62Ni, 58Fe and 60Ni, all of which have a very high binding energy.


The isotope 57Fe is widely used in Mössbauer spectroscopy due to the low natural variation in energy of the 14.4keV nuclear transition.[3]


Iron-60 is an iron isotope with a half-life of 2.6 million years,[4][5] but was thought until 2009 to have a half-life of 1.5 million years. It undergoes beta decay to cobalt-60.

In phases of the meteorites Semarkona and Chervony Kut a correlation between the concentration of 60Ni, the granddaughter isotope of 60Fe, and the abundance of the stable iron isotopes could be found which is evidence for the existence of 60Fe at the time of formation of the solar system. Possibly the energy released by the decay of 60Fe contributed, together with the energy released by decay of the radionuclide 26Al, to the remelting and differentiation of asteroids after their formation 4.6 billion years ago. The abundance of 60Ni present in extraterrestrial material may also provide further insight into the origin of the solar system and its early history.


Z(p) N(n)  
isotopic mass (u)
half-life decay
mode(s)[6][n 1]
isotope(s)[n 2]
(mole fraction)
range of natural
(mole fraction)
excitation energy
45Fe 26 19 45.01458(24)# 1.89(49) ms
β+ (30%) 45Mn 3/2+#
2p (70%) 43Cr
46Fe 26 20 46.00081(38)# 9(4) ms
[12(+4-3) ms]
β+ (>99.9%) 46Mn 0+
β+, p (<.1%) 45Cr
47Fe 26 21 46.99289(28)# 21.8(7) ms β+ (>99.9%) 47Mn 7/2-#
β+, p (<.1%) 46Cr
48Fe 26 22 47.98050(8)# 44(7) ms β+ (96.41%) 48Mn 0+
β+, p (3.59%) 47Cr
49Fe 26 23 48.97361(16)# 70(3) ms β+, p (52%) 48Cr (7/2-)
β+ (48%) 49Mn
50Fe 26 24 49.96299(6) 155(11) ms β+ (>99.9%) 50Mn 0+
β+, p (<.1%) 49Cr
51Fe 26 25 50.956820(16) 305(5) ms β+ 51Mn 5/2-
52Fe 26 26 51.948114(7) 8.275(8) h β+ 52Mn 0+
52mFe 6.81(13) MeV 45.9(6) s β+ 52Mn (12+)#
53Fe 26 27 52.9453079(19) 8.51(2) min β+ 53Mn 7/2-
53mFe 3040.4(3) keV 2.526(24) min IT 53Fe 19/2-
54Fe 26 28 53.9396105(7) Observationally Stable[n 3] 0+ 0.05845(35) 0.05837-0.05861
54mFe 6526.9(6) keV 364(7) ns 10+
55Fe 26 29 54.9382934(7) 2.737(11) a EC 55Mn 3/2-
56Fe[n 4] 26 30 55.9349375(7) Stable 0+ 0.91754(36) 0.91742-0.91760
57Fe 26 31 56.9353940(7) Stable 1/2- 0.02119(10) 0.02116-0.02121
58Fe 26 32 57.9332756(8) Stable 0+ 0.00282(4) 0.00281-0.00282
59Fe 26 33 58.9348755(8) 44.495(9) d β- 59Co 3/2-
60Fe 26 34 59.934072(4) 2.6×106 a β- 60Co 0+ trace
61Fe 26 35 60.936745(21) 5.98(6) min β- 61Co 3/2-,5/2-
61mFe 861(3) keV 250(10) ns 9/2+#
62Fe 26 36 61.936767(16) 68(2) s β- 62Co 0+
63Fe 26 37 62.94037(18) 6.1(6) s β- 63Co (5/2)-
64Fe 26 38 63.9412(3) 2.0(2) s β- 64Co 0+
65Fe 26 39 64.94538(26) 1.3(3) s β- 65Co 1/2-#
65mFe 364(3) keV 430(130) ns (5/2-)
66Fe 26 40 65.94678(32) 440(40) ms β- (>99.9%) 66Co 0+
β-, n (<.1%) 65Co
67Fe 26 41 66.95095(45) 394(9) ms β- (>99.9%) 67Co 1/2-#
β-, n (<.1%) 66Co
67mFe 367(3) keV 64(17) µs (5/2-)
68Fe 26 42 67.95370(75) 187(6) ms β- (>99.9%) 68Co 0+
β-, n 67Co
69Fe 26 43 68.95878(54)# 109(9) ms β- (>99.9%) 69Co 1/2-#
β-, n (<.1%) 68Co
70Fe 26 44 69.96146(64)# 94(17) ms 0+
71Fe 26 45 70.96672(86)# 30# ms
[>300 ns]
72Fe 26 46 71.96962(86)# 10# ms
[>300 ns]


  • Values marked # are not purely derived from experimental data, but at least partly from systematic trends. Spins with weak assignment arguments are enclosed in parentheses.
  • Uncertainties are given in concise form in parentheses after the corresponding last digits. Uncertainty values denote one standard deviation, except isotopic composition and standard atomic mass from IUPAC which use expanded uncertainties.
  • Nuclide masses are given by IUPAP Commission on Symbols, Units, Nomenclature, Atomic Masses and Fundamental Constants (SUNAMCO)
  • Isotope abundances are given by IUPAC Commission on Isotopic Abundances and Atomic Weights

See also


  • Isotope masses from:
  • Isotopic compositions and standard atomic masses from:
  • Half-life, spin, and isomer data selected from the following sources. See editing notes on this article's talk page.

Further reading

Isotopes of manganese Isotopes of iron Isotopes of cobalt
Table of nuclides
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